高动态环境下扩频系统的快速同步方案

提出了一种应用于高动态环境下扩频系统的快速同步方案,通过优化帧结构设计,利用PN序列自相关达到快速的帧捕获,通过对鉴频环路的结构修改,采用FLL和PLL协同工作的方式,利用四相鉴频器跟踪频率变化,进行大频率搜索;利用叉积自动频率跟踪算法联合Costas环作为载波跟踪算法;环路滤波器采用扩展卡尔曼滤波技术,在提升信号捕获速率的同时,降低噪声的影响,提高捕获精度。经仿真验证,可以在相对较低的复杂度下获得良好的性能。     

A fast adaptive resonance suppression scheme for high-damping system using R-SDFT detection

Adaptive notch filter resonance suppression scheme is widely used in high-performance servo drivers. For high-damping system, the deviation between resonant and oscillation frequency will cause a long sustained vibration in traditional suppression schemes, which may damage the precision machine irreparably. To reduce the harm of sustained vibration, a fast adaptive notch filter scheme based on range-shifted discrete Fourier transform (R-SDFT) is proposed. Different from the traditional scheme, the new one eliminates the deviation between resonant and oscillation frequency by notch filter other than the low-pass filter, which massively simplifies the suppression process and reduces the number of oscillation frequency detection required. Meanwhile, an oscillation detection method based on R-SDFT is presented to shorten the time of the detective process through interval detection and prediction strategy. Compared with the traditional strategy, the experimental results demonstrate that the proposed adaptive suppression scheme can reduce the oscillation time by more than half.     

A fast iterative scheme for multilevel thresholding methods

The previously published optimal thresholding techniques based on some objective functions are very efficient in the bi-level thresholding case, but they are impractical when extended to multilevel thresholding. The reason for this is their computational complexity which grows exponentially with the number of thresholds. In this paper, an iterative scheme is proposed to render these optimal thresholding techniques more practical. The proposed algorithm starts with a bi-level thresholding, then uses the initial results to obtain higher-order thresholds. This algorithm is iterative and the convergence is proved. We also introduce some useful programming techniques to make the computation more efficient. The proposed algorithm can therefore determine the number of thresholds automatically as well as save a significant amount of computing time.     

A fast video-on-demand broadcasting scheme for popular videos

Broadcasting is a prospective approach to support near video-on-demand services with light communication overhead. By letting clients share channels, such approaches involve partitioning a video into segments and repeatedly broadcasting these segments in multiple channels. An early paper proposed a broadcasting scheme called RFS (recursive frequency splitting), which can significantly reduce clients' waiting time. While efficient, RFS suffers from a high computational complexity of O(nlogn), where n is the number of segments of the video, which is typically very large. This paper proposes an efficient segmentation scheme, which can significantly reduce the computational overhead by slightly sacrificing the number of segments that can be arranged as compared to RFS.     

A diversity scheme for a phase-coherent frequency-hoppingspread-spectrum system

Frequency diversity for a phase-coherent frequency-hopping spread-spectrum system is proposed. The frequency band of the communicator is partitioned into L disjoint subbands on which L replicas of the communicator signal are simultaneously transmitted; each signal replica hops independently in its subband. Therefore, both phase continuity and coherent optimal combining of the received replicas are possible. Optimum diversity is thus at least 6 dB better than the conventional noncoherent FH-SS system. We show that a smart jammer should be present in all subbands. We also give a sufficient condition that forces the jammer to spread its interference signal on the whole communicator frequency band     

A fast multicast IP-routing lookup scheme

This paper proposes a fast multicast IP-routing lookup scheme, which adopts a compression bit map conception for forwarding information. The proposed scheme can achieve fast address lookup speed and reasonable forwarding table size.     

A fast IP routing lookup scheme

A major issue in router design for the next generation Internet is the fast IP address lookup mechanism. The existing scheme by Huang et al. (see Proc. IEEE INFOCOM'99, New York, NY, 1999) performs the IP address lookup in hardware in which the forwarding table can be compressed to fit into a reasonable-size SRAM, and a lookup can be accomplished in three memory accesses. We claim that with a little extra memory, it is able to further reduce the lookup time to two memory accesses     

A low-cost unrestricted fast playback scheme for video streaming

In this brief, we propose a low cost fast-forward and fast-backward playback scheme for video streaming applications. By reshaping the ordinary linear encoded group-of-pictures (GOP) structure into a hierarchical structure, the transmission overhead caused by frame dependencies can be reduced. The resulting video streaming system can provide all directions video playback with any speed-up factor. A set-top box architecture that supports the binary tree structured GOP playback is also described.     

A low-power fast tag comparator by modifying charging scheme of wide fan-in dynamic OR gates

In this paper, a new charging scheme for reducing the power consumption of dynamic circuits is presented. The proposed technique is suitable for large fan-in gates where the dynamic node discharges frequently. Simulation results demonstrate that the proposed method is efficiently controlling the internal voltage swing and hence decreasing the power consumption of the wide fan-in OR gate without sacrificing other circuit parameters such as gate speed, area or noise immunity. The power-delay product of a simulated 8-input OR gate is reduced by 46%, compared to its conventional dynamic counterpart in the 90 nm CMOS technology. Another important benefit of the proposed approach is 99X reduction in power dissipation of the gate load by limiting its switching activity. Furthermore, the delay of the proposed circuit experiences only 0.94% variation over 10% fluctuation in the threshold voltages of all transistors for a 32-bit OR gate. Using the proposed technique, a 40-bit tag comparator is simulated at 1 GHz clock frequency. The power consumption of the designed circuit is as low as 1.987 µW/MHz, while the delay and unity noise gain (UNG) of the circuit are 244 ps and 499 mV, respectively.     

A new realization scheme for dynamic PFSCL style

In this paper, a new scheme of logic function realization in dynamic positive feedback source-coupled logic (D-PFSCL) style is proposed. The existing scheme implements only NOR/OR based realization of a logic function. Thus, a complex function in D-PFSCL has high gate count which degrades the overall circuit performance measured in terms of power and delay. This paper therefore aims to resolve the issue by proposing a scheme which modifies the structure of a D-PFSCL gate. The modified gate exhibits AND/OR functionality and is used to realize various functions. Simulations have been carried out by implementing various functions and comparing their performance with the existing schemes at 1 GHz. The results of performance comparison with existing schemes indicates significant reuduction in gate count resulting in overall performance improvement.     

高速DS/FH系统中的能量检测辅助同步方法

同步是高速DS/FH混合扩频系统的关键技术之一。针对高速DS/FH混合扩频系统的需求,提出了一种快速同步方法,通过在随时间变化的同步信道上传输同步信息,并通过能量检测辅助等待搜索的方式捕获同步信号。数学分析表明,此方法用较少的系统资源,获得了较短的捕获时间和较强的抗干扰性能。     

Candidate scheme for fast ACELP search

The algebraic code excited linear prediction (ACELP) algorithm has been adopted by many speech coding standards, due to low complexity and high quality in its analysis-by-synthesis optimisation. For further computational complexity reduction, the authors propose a fast ACELP algorithm using a designed pilot function to predict the predetermined candidate pulses. With candidate pulses, it is possible to not only reduce the number of search loops but also to avoid the computation of unnecessary correlation functions. The proposed candidate position scheme can be applied to all ACELP coders such as the ITU G-723.1 and G.729 as well as the GSM enhanced full rate (EFR) speech coding standards. Simulation results show that the computational load can be reduced by about 50-80% with almost imperceptible degradation in performance     

A self-timed divider using a new fast and robust pipeline scheme

This paper investigates the potential of self-timed property of differential cascode voltage switch logic (DCVSL) circuits, and examines architectural techniques for achieving self-timing in DCVSL circuits. As a result, a fast and robust handshake scheme for dynamic asynchronous circuit design is proposed. It is novel and more general than other similar schemes. The proposed self-timed datapath scheme is verified by an 8-bit divider which is implemented using AMS 0.6-μm CMOS technology, and the chip size is about 1.66 mm×1.70 mm. The chip testing results show that the divider functions correctly and the latency for 8-bit quotient-digit generation is 17 ns (about 58.8 MHz)     

A novel key management scheme for dynamic multicast communications

Secure multicasting allows the sender to deliver an identical secret to an arbitrary set of recipients through an insecure broadcasting channel, whereas the unintended recipients cannot obtain the secret. A practical approach for securing multicast communications is to apply a session key to encrypt the transmitted data. However, the challenges of secure multicast are to manage the session keys possessed by a dynamic group of recipients and to reduce the overhead of computation and transmission when the membership is changed. In this paper, we propose a new key management scheme for dynamic multicast communication, which is based on privacy homomorphism and Chinese remainder theorem. Our scheme can efficiently and securely deliver an identical message to multiple recipients. In particular, the complexity of the key update process in our scheme is O(1). Copyright © 2008 John Wiley & Sons, Ltd.     

A dynamic location management scheme for next-generation multitierPCS systems

Global wireless networks enable mobile users to communicate regardless of their locations. One of the most important issues is location management in a highly dynamic environment because mobile users may roam between different wireless systems, network operators, and geographical regions. A location-tracking mechanism is introduced that consists of intersystem location updates and intersystem paging. Intersystem update is implemented by using the concept of boundary location area, which is determined by a dynamic location update policy in which the velocity and the quality of service are taken into account on a per-user basis. Also, intersystem paging is based on the concept of a boundary location register, which is used to maintain the records of mobile users crossing the boundary of systems. This mechanism not only reduces location-tracking costs, but also significantly decreases call-loss rates and average-paging delays. The performance evaluation of the proposed schemes is provided to demonstrate their effectiveness in multitier personal communication systems     

一种新的基于GPON的动态带宽分配算法

为了实现吉比特无源光网络(GPON)带宽分配的公平性,降低网络的丢包率及传输延时,文章研究了GPON系统传输汇聚层的帧结构及动态带宽分配的实现方法,提出了一种新的动态带宽分配(DBA)算法--基于QoS的二层动态带宽分配算法.基本思路是根据不同等级业务的带宽需求,在PON层和ONU层分别进行带宽的合理分配.理论分析和仿真试验证明,这种算法可以提高带宽的利用率,保证不同业务的不同时延要求,并且对不同用户和不同等级的业务都具有很好的公平性.     

协作频谱感知中的动态信任评估机制

针对动态性SSDF攻击对协作频谱感知技术的危害性,实时观察分析认知用户的感知行为,提出一种动态信任评估机制.根据认知用户的历史感知变化情况,引入时间衰减因子、加性奖励因子和加性惩罚因子,计算出随时间和协作次数不断变化的动态信任值,选取可信认知用户参与协作感知,提高了数据融合中心的协作判决准确性.仿真结果表明,动态信任机制可以有效抑制恶意用户的信任值增长,降低对“OR”、“AND”和“Majority”3种常用协作频谱感知数据融合准则的攻击成功率.     

A dynamic regulation and scheduling scheme for real-time trafficmanagement

Typical rate-based traffic management schemes for real-time applications attempt to allocate resources by controlling the packet delivery to the resource arbitrator (scheduler). This control is typically based only on the characteristics of the particular (tagged) traffic stream and would fail to optimally adjust to non-nominal network conditions such as overload. In this paper, a dynamic regulation and scheduling (dynamic-R&S) scheme is proposed whose regulation function is modulated by both the tagged stream's characteristics and information capturing the state of the coexisting applications as provided by the scheduler. The performance of the proposed scheme-versus an equivalent static one-is investigated under both underload and overload traffic conditions. The substantially better throughput/jitter characteristics of the dynamic-R&S scheme are established     

A PCE-based dynamic backup-reservation wavelength assignment scheme for WSONs

For the Destination Initialed Reservation in PCE-based Wavelength Switched Optical Networks using the distributed wavelength assignment scheme, the establishment of a lightpath might be blocked because of the contention for the same wavelength between two or more concurrent requests traversing the same links, although there might be enough wavelength resource available. In order to reduce the blocking caused by contention, in the PCE-based architecture a Dynamic Backup-reservation Wavelength Assignment (DBWA) scheme has been proposed in this paper. Considering that it is not an advisable way to reserve additional wavelength when the resource is lacking and meanwhile a lightpath with more physical hops has higher probability to collide with others, a threshold is defined to decide whether to reserve a backup wavelength or not. Simulation results show that, by setting a proper value for threshold, DBWA can reduce the contention-induced blockings efficiently in comparison with the two traditional schemes.